This invention pertains to the art of hydromechanical servo systems, and more particularly to such a system having mechanical feedback.
Hydromechanical servo systems often exhibit dynamic performance which is marginally stable or unstable. This is usually due to intercoupling of the load mass with spring rates of structures and hydraulic fluid which are part of the servo systems.
Stability margins may be improved by various methods. One method which is highly effective and imposes little or no penalty in system weight or performance involves the use of structural feedback compensation. This method is widely used in aircraft flight control servo systems and is described in a paper entitled "Improvement of Power Surface Control Systems By Structural Defelection Compensation" by James J. Rahn and Everett W. Kangas, published in Report of the Second Piloted Aircraft Flight Control System Symposium by Bu Aer, Report No. AE-61-5, June, 1952, Volume III, page 107.
Recently, extreme emphasis has been placed upon assuring "survivability" of military aircraft flight control integrity. One means toward this end includes incorporation of detent means in the control linkage of flight control servo units.
In the event that the mechanical linkage path from cockpit to servo unit is disconnected, due to failure or due to battle damage, such a detent would hold the servo unit, and thus the flight control surface, in a preferred passive position. However, this detented or "fail-safe" condition, with normal linkage path disconnected, renders the structural feedback compensation inoperative and the system may now be marginally stable or unstable.